1. Field of the Invention
The present invention relates to telephony. In particular, the present invention relates to eliminating or minimizing the transition that occurs when real background noise is replaced by comfort noise in a voice over IP terminal such as a voice over IP analog or digital gateway, or voice over IP telephones.
2. The Prior Art
Background
The widespread acceptance and use of the internet has generated much excitement, particularly among those who see the Internet as a possible substitute for the traditional telephone system. As the backbone of the Internet continues to be upgraded and expanded, the promise of a low-cost substitute to the traditional PBX system may now be realized.
One type of Internet-based telephony system that is gaining acceptance is IP telephony, which transfers voice information over the Internet Protocol (IP) of the TCP/IP protocol suite. While many standards exist, such as Voice over Packet (VOP) for Frame Relay and ATM networks, as used herein the term “IP telephony” will be used to designate voice over any packet-based network. In IP telephony, a user wishing to communicate uses an IP telephone, which is a device which transports voice over a network using data packets instead of the traditional switched circuits of a voice only network.
FIG. 1 shows an IP telephony system 100 of the prior art. System 100 includes a business system 102 configured to provide IP telephony in an enterprise environment. Business system 102 may include a network 104, such as a corporate Ethernet LAN, to which a plurality of IP telephones 106 may be operatively coupled to network 104 using hardware and software standard in the art. To couple the business system 102 to the outside world, typically a gateway 108 standard in the art is provided and operatively coupled between network 104 and backbone network 110.
Backbone network 110 may be any packet-based network standard in the art, such as IP, Frame Relay, or ATM. To provide voice communications to legacy POTS phones, typically a gateway 112 is provided, which may be a VoP gateway. Gateway 112 provides access to the Public Switched Telephone Network (PSTN) 114. Through PSTN 114, voice-only communications may be provided to legacy POTS phones 116.
The system 100 of FIG. 1 also includes an example of a broadband residential system 118. To reach individual residences, typically local ISP providers provide a cable or DSL head end 120 standard in the art. An individual wishing to utilize the ISP's service may then employ a cable modem or DSL modem 122 coupled to the user's home LAN 124. The user's home LAN may be provided by a home PC 126 configured to run software standard in the art such Microsoft Windows®. The user may then operatively couple an IP telephone 128 to the LAN 124.
Thus, in the system 100 of FIG. 1, IP telephones 106 in business system 102 may communicate by voice with other similar business systems similarly configured with IP telephones. For a business enterprise, communication by IP telephony may be advantageous because the need for a traditional PBX system can be eliminated. Furthermore, an IP telephony system is scalable and may be upgraded along with the enterprise's network system.
Likewise, the residence of system 118 may communicate by voice to a POTS phone 116 using 1P telephone 128. From the view of the home user, the communication of FIG. 1 is advantageous because the communication operates over the backbone network 110 without accessing traditional long-distance service providers.
FIG. 2 is conceptual block diagram of a prior art IP telephone system 200 including a TX unit 202 of a transmitting IP telephone standard in the art and a RX unit 204 of a receiving IP telephone standard in the art. TX unit 202 and RX unit 204 are shown operatively coupled to each other through a network cloud 216. For the sake of clarity, elements of a typical IP telephone not essential to the explanation of the present invention are not shown in the disclosure.
TX unit 202 includes a microphone 206 coupled to a Voice Activity Detector (VAD) 208, a silence indication packet generator 212 and an encoder 214. VAD 208, encoder 214, and silence indication packet source 212 are operatively coupled to each other to provide an output for transmission over network 216.
In operation, the VAD 208 will determine whether there is voice activity present in the signal coming from microphone 206 using methods known in the art. If there is voice activity in the signal, the switching logic will pass the output of the encoder (i.e., a packet stream) for transmission to network cloud 216 using methods standard in the art.
If the VAD 208 determines that there is no voice activity present on the signal coming from microphone 206, then the switching logic 210 will send one or more silence indications packets to network cloud 116. The silence indication packets contain at least a background noise level so that the comfort noise generator 218 on the receive side can generate noise similar in level and character to the actual background noise on the transmit side.
Comfort noise is a prior art solution to save network bandwidth. The prior art methods determined that if there is no voice activity present, then no voice packets should be sent over the network. However, this results in an unnatural silence appearing on the receiving unit, since no packets are being sent. As a result, the prior art methods developed the concept of comfort noise, which presents the listener with generated noise designed to mimic the line noise of traditional legacy telephones when there is no voice activity present. The comfort noise reassures listeners that their connection is still active. As used herein, comfort noise will be used to designate a more specific type of packet than background noise.
Referring still to FIG. 2, RX unit 204 includes a comfort noise generator 218 operatively coupled to a decoder 220. The comfort noise generator 218 and decoder 220 are both operatively coupled to switching logic 224. When the output of TX unit 202 has been transmitted over network 216, it will be received by RX unit 204, and presented to a decoder 220 and a comfort noise generator 218 using methods standard in the art.
If the switching logic receives an encoded voice packet it routes it to the decoder which then outputs the decoded audio signal to the speaker 226. If the switching logic receives a silence indication packet it routes the comfort noise generator 218 which then generates comfort noise to the speaker 226 until further voice packets are received. Typically, the CF comprises white or pink noise.
While the systems of FIGS. 1 and 2 perform well for there intended purpose, some disadvantages have been encountered when compared to legacy phone systems. For example, some users of IP telephones have reported inconveniences when using an IP telephone and periods of silence occur.
FIG. 3 is a prior art conceptual diagram showing IP telephony data flow received by a receiving unit. The blocks of FIG. 3 represents the information present during time intervals T1 through T4.
In time interval T1, the receiving unit may be receiving voice information while engaging in a conversation. When the conversation quiets down, the receiving unit may then receive real background noise in time interval T2.
However, in prior art systems, if no voice information is present for a predetermined time, then the TX unit will begin to send comfort noise packets in time interval T3.
Finally, the conversation may resume in time interval T4, and the receiving unit will again hear voice information. Thus, the listening parties utilizing IP telephones of the prior art will perceive an abrupt transition between real background noise and comfort noise in the transition from time interval T2 to time interval T3. This transition typically sounds unnatural because comfort noise rarely models the actual background noise very well. Typically many highly noticeable frequency components will be missing. The transition between interval T3 and T4 is less noticeable as the listener tends to focus on the voice of the speaker rather than the background noise.
Hence there is a need for a method and apparatus to eliminate or minimize the transition that occurs when real background noise is replaced by comfort noise in an IP telephone.